Cycloparaffin production



Jan. 28, 1947. 'w oss ET CYCLOPARAFFIN PRODUCTION Filed July 17, 1944WuGELJ lnveni-orsz William E. Ross Philip Pezzagh'a. Bgiheir Afiorneg:

Patented 1.... 2a, 1941 FICE crcaoraaarrm' raonUc'rroN William E. Ross,Berkeley, and Philip Pcuaglia, Oakland, Calif., assl'gnors toShellDevclopment Companm san Francisco, Calif acorporation ot'DelawareApplication July 17, 1944, Serial No. 545,349

7 Claims. (o1. com-ass) This invention relates to the production of.

cycloparafiins of hydr'oaroma'tic structure from hydrocarbon mixtures ofrelatively wide boiling range such as naphthenic gasolines or fractionsthereof comprising cycloparafiins of hydroaromatic and non-hydroaromaticstructure in admixture with open chain paraflinic hydrocarbons. Theinvention relates more particularly to an improved process for the moreeilicient'production of cyclohexane. from naphthenic gasolines andfractions thereof comprising methylcyclopentane and cyclohexane.

The cycloparaflins ofhydroaromatic structure, particularly cyclohexane,are of great value as starting materials and intermediates in theproduction of a wide variety of organic products. A most fertile sourceof these highly desirable materials resides in the naturally occurringhydrocarbon mixtures of naphthenic character such as naphthenic, naturaland straight run gasolines, etc. Other sources comprise hydrocarbonmixtures of naphthenic character boiling in the gasoline boiling rangeobtained by fractionation of the products of many of the processesinvolving the catalytic or thermal treatment of hydrocarbons orcarbonaceous materials. As is well known, these readily availablehydrocarbons constitute highly complete mixtures of a plurality ofindividual hydrocarbons, many of which have similar or closelyapproximating boiling points and many of which are capable of forming.azeotropes with one another during distillation. Realization of the fulladvantages inherent in the many chemical processes relying upon thecycloparafiins ofhydroaromatic structure as starting or intermediatematerials has been handicapped by the lack of a process enablingefiicient production of the cycloparaffins of hydroaromatic structure ona practical scale from these available complex mixtures. Not only is itimperative that such cycloparaffins of hydroaromatic structures be.produced with high yields, but itis essential that the product obtainedbe of a relatively high purity and yet involve the use of a minimum ofoperative steps.

. paraflinic hydrocarbons inseparable therefrom by Efiicient productionof a cycloparaffin of hydro-.

cycloparafiins or non-hydroaromatic structure such as methylcyclopentaneto cyclohexane. Separation of either or both of these cycloparaflinsfrom the complex hydrocarbon mixtures in which they are generallyencountered, by such methods as fractional distillation, if at. allpossible, is often rendered so involved and delicate an operation as torender it highly impractical. By the term hydroaromatic cycloparamnsf,as used throughout this specification and appended claims is meant thecycloparafiins having a hexamethylene I ring such as, for example,cyclohexaneand the alkyl cyclohexanes, to distinguish them fromcycloparaffins of non-hydroaromatic structure com-. prisingthose'havi'ng pentamethylene rings such as, for example,methylcyclopentane and other alkyl cyclopentanes.

It is an object of the present invention to provide an improved processfor the more eflicient production of cycloparaflins oi hydroaromaticstructure from hydrocarbon mixtures of relatively wide boiling rangesuch as naphthenic gasolines or fractions thereof comprisingcycloparafiins of hydroaromatic and non-hydroaromatic structure inadmixture with open chain paraflin hydrocarbons of substantially thesame boiling range.

Another object of the invention is theprovision of an improved processfor the more efiicient pro-- duction of cyclohexane from hydrocarbonmixtures of relatively wide boiling range such as naphthenic gasolines.

Still another-object of the invention is to provide an improved processfor the more efficient production of cyclohexane from naphthenicgasoline fractions comprising methylcyclopentane and cyclohexane inadmixture with open chain fractionating means. 'Other objects andadvantagesof the invention will become apparent from the followingdescription thereof. 1

In accordance with the process of the invention a hydrocarbon mixture ofnaphthenic character from any suitable source such as, for example, anaphthenic straight run gasoline is subjected to fractionation toseparate therefrom a fraction comprising cycloparaflins ofnon-hydroaromatic and hydroaromatic structure in admixture with openchain paraflins of substantially the same boiling range. The fractionthus obtained is subjected to isomerizing conditions to effect theconversion of cycloparaiiins of non-hydroaromatic structure tocycloparaffins of hydroaromatic structure. The resulting isomerizate issubjected to fractionation to separate therefrom a fraction comprisingcycloparaflins of non -hydroaromatic structure which is recycled to theisomerization reactor and a fraction comprising cycloparafiins ofhydroaromatic structure in admixture with open chain paraffins ofsubstantially the same boiling range. The fraction comprisingcycloparaffins of hydroaromatic structure thus separated from theisomerizate is subjected to controlled thermal cracking conditions toeffect the substantially selective cracking of open chain paraflins tolower boiling hydrocarbons readily separable from the cycloparaffins.The

resulting products are fractionated to separate.

a fraction comprising cycloparaffins of hydrosalts.

aromatic structure of high purity. As will be apparent from thefollowing detailed description thereof, the invention enables not onlythehighly officient production of .cycloparaffins of hydroaromaticstructure from natural gasolines on a practical scale, but enables theobtaining of the desired product on a large scale in a greater state ofpurity. v

In order to set forth more fully the nature of the invention it will bedescribed herein in detail in its application to the production ofcyclohexane from hydrocarbon mixtures of naphthenic character in thegasoline boiling range, with reference to the attached drawing in whichthe single figure represents a more or less diagrammatic elevationalview of one form of apparatus suitable for executing the process of theinvention.

A hydrocarbon-mixture of naphthenic character such as, for example. anaphthenic straight run gasoline, is forced through valved line I into-a feed fractionatorl, Within feed fractionator 2 a fraction comprisingmethylcyclopentane and cyclohexane is separated and forced throughvalved line 3 into a, conversion zone comprising,

for example, reactor 4. Thefraction separated in fractionator 2 andpassed into reactor 4 is of sufficiently wide boiling range to comprisesubstantially all of the methyl cyclopentane and cyclohexane originallypresent in the straight run gasoline. A fraction boiling in the range offrom about 65 C. to about 85 C. has been found particularly desirable.Such a fraction will unavoidably comprise a number of hydrocarbons otherthan methylcyclopentane and cyclohexane, such as normal hexane, somebenzene, and particularly, branched chain heptanes such as2,2-dimethylpentane and 2,4-dimethylpentane, inseparable fromcyclohexane by fractionating means. Although it is preferred to separateand pass to reactor 4 a fraction boiling in the range of from about 65C. to about 85 C., a fraction comprising a somewhat wider boiling rangemay suitably be employed. A naphthenic gasoline fraction comprisingmethylcyclopentane and cyclohexane from anyother source may beseparately introduced through valved line 5 into line 3 and may comprisea part or all of the charge to the system.

Within reactor-f4 the hydrocarbon fraction is contacted undercycloparafiin isomerizing conditions with an isomerization catalyst.catalysts comprise those containing a. metal halide of theFriedel-Crafts type, particularly those com? the organo-aluminum halidecomplexes, preferably a preformed aluminum chloride hydrocarbon complex.Other suitable catalysts comprise those of the molten salt typecontaining the aluminum halide in .admixture with one or more halide Thetemperature in reactor 4 is maintained in the range of from about 20 C.to about 100 C. and preferably from about C. to about 90 C. Theparticular temperature chosen within this specified temperature rangewill be governed to at least a substantial degree by the particularcatalyst employed. When utilizing a preformed aluminum halidehydrocarbon complex as the catalyst a temperature in the range of fromabout 65 C. to about 85 C. is somewhat preferred. A

hydrogen halide promoter such as, for example, a

Suitable of Table I.

, 4 0.5 to about 2% by weight of the hydrocarbon charge to theconversion zone. Higher or lower concentrationsof the hydrogen chloridemay at times be desirable depending upon variation in operatingconditions. Under these conditions methylcyclopentane will be convertedto cycloing by the single fractionator 15. Within frac-' tionator 15there are separated a fraction comprising material lower boiling thancyclohexane and including unconverted methylcyclopentane; a cyclohexaneconcentrate; and liquid bottoms comprising materials higher boiling thancyclohexane. The fraction comprising methylcyclopentane is removedoverhead through line I! and recycled at least in part to reactor 4 bymeans of line l8. The stream thus recycled may be subjected to afractionation to effect the separation of hydrocarbons other thanmethylcyclopentane therefrom prior to passage to the conversion zone.The cyclohexane concentrate, separated in fractionator l5, boiling, forexample, in the range of from about 75 C. to about 85 C. will comprise,besides cyclohexane, some benzene and branched chain heptanesinseparable from cyclohexane by fractionating means. The cyclohexaneconcentrate is taken from an intermediate part of fractionator i5 andpassed through line 20 to a thermal cracking zone. example isillustrative of the production of the cyclohexane concentrate inaccordance with the process of the invention.

Example I fraction thus obtained is given in column A of the followingTable I. The hydrocarbon fraction was isomerized by contact with apreformed aluminum chloridehydrocarbon complex at a temperature of C.with a contact time of 26 minutes. Hydrogen chloride in an amount equalto 1% by weight of the charge was added. The composition of theisomerizate is given in column B of Table I. The isomerizate wasfractionally distilled to separate therefrom a cyclohexane concentrateboiling in the range of from 75 C. to C. and a lighter boiling fractioncomprising methylcyclopentane for recycling to the isomerization zone.The composition of the cyclohexane concentrate thus obtained is given incolumn C C cyclohexane B Isomerizate concentrate sesame The following Itis seen from the foregoing example that the cyclohexane concentrateproduced contains only 88% cyclohexane and includes 7% dimethylpentanesdiilicult to separate therefrom by fractionation or other means. Such aproportion of open chain paraffins is substantially above that to]-erated in many of the processes wherein cyclohexane is utilized asstarting or intermediate material. Reduction of the open chain paraffincontent of such a fraction on a large scale would be so costly as torender the process economically unfeasible. In accordance with theprocess of the invention, however, the open chain paraflins areseparated eiliciently resulting in the produc-- tion of a cyclohexane ofhigh purity in a minimum of operative steps.

The thermal cracking zone to which the cyclo-' hexane concentrate ispassed through line 20 may comprise an externally heated elongated coil23 positioned within a furnaced structure 24. Prior to passage into coil23 the cyclohexane is preferably subjected to a treatment, by means notshown in the drawing, to effect the removal of benzene therefrom. Suchtreatment may comprise scrubbing with sulfuric acid or a selectivesolvent for the aromatic hydrocarbon or any othersuitable'means. Theresulting cyclohexane concentrate, substantially free of benzeneybutstill comprising the open chain paraflins is passed into coil 23.

Within coil 23 the cyclohexane concentrate is subjected to a temperaturein the range of from about 500 C. to about 700 C. and preferably fromabout 550 C. to about 650 C. The stream is preferably maintained in thistemperature range for a period of time of from about 5 seconds to about30 seconds and preferably from about 10 seconds to about 20 seconds.Under these conditions open chain paraffi'ns comprising the open chainheptanes are substantially selectively cracked to lower boilinghydrocarbons readily sep-' arable from cyclohexane. From coil 23 thecracked stream is passed through valved line 25 into fractionator 26. Avalved lin 21 is provided for the introduction of a suitable quenchingmedium into line 25. Within column 26 there is separated overhead avapor fraction comprising material lighter boiling than cyclohexane.Bottoms, comprising cyclohexane and a relatively small amount ofmaterial higher boiling than cyclohexane, are passed from column 28through line 29 into iractionator 30. Within column 30 cyclohexanecomprising a substantially reduced amount of open chain paraflinsboiling at or near the boiling point of cyclohexane is taken as anoverhead product through line 32. Products resulting from the crackingof the open chain paraf-,

comprising, for example, scrubbing with a selective solvent or acidassulfuric acid, by means not shown in the drawing, to assure the removalor unsaturated hydrocarbons therefrom.

In the prefered method of execution of the process of the invention, thehydrocarbon fraction passed to cracking coil 23 will comprisesubstantially only cycloparafilns of hydroaromatic structure. At least asubstantial part of the separated from the cracked products as-aseparate than 95% purity.

fraction within column and recycled therefrom through line 33 to theisomerization zone.

Example II The cyclohexane concentrate separated from the isomerizateand the composition of which is given in column C of Table I wasscrubbed with sulfuric acid to remove the benzene therefrom. Theresulting benzene free hydrocarbon mixture was then washed with a dilutecaustic solution to remove any acidic constituents therefrom. Theresulting cyclohexane concentrate now substantially free of benzene wassubjected to selective paraflin cracking at a temperature of 600 C. anda contact time of from 9 to'12 seconds. 43% of the dimethyl pentanepresent in the charge to the cracking zone was thereby converted tomaterial substantially lower boiling than cyclohexane and readilyseparable therefrom. Distillation and acid treatment of the productsfrom the cracking zone yielded cyclohexane of better It is apparent fromthe foregoing that the invention provides a highly efficient method forthe production of cyclohexane with a minimum of cyclohexane thus beingproduced not only with high yields, but in a high state of purity freeof any substantial amount of highly undesirable branched chain heptanes.genenlly present in cyclohexanes produced by methods availableherecycioparafiins of non-hydroaromatic structure present in the'isomerizate may, however, be included. When operating in this mannerthe cycloparaflins or non-hydroaromatic structure are tofore.

The above-detailed illustrative description of the invention has beendirected to the production of cyclohexane. The invention is, however,not limited to the production of only this cycloparaflin ofhydroaromatic structure and may be applied with advantage to theproduction of other cycloparaffins of hydroaromatic structure fromcomplex naphthenic hydrocarbon mixtures. Thus, the process of theinvention is applied to the production of methylcyclohexane from anaphthenic gasoline by separation therefrom of a fraction comprisingcycloparaflins of non-hydroaromatic and hydroaromatic structure havingseven carbon atoms to the molecule, such as dimethylcyclopentane andmethylcyclohexane respectively, and the parafiinic .hydrocarbons ofclose boiling range inseparable therefrom by fractionation on apractical scale. The fraction thus obtained is isomerized as describedabove in isomerization zone 4 and a fraction predominating incycloparafiins of hydroaromatic structure is separated from theresulting isomerizate. The fraction comprising the cycloparafilns ofhydroaromatic "structure thus obtained and unavoidably comprising openchain paraiiins inseparable therefrom by fractionation is subjected tothermal selective paraflln cracking conditions thereby eonverting theopen chain parafil.ns to lower boiling products readily separable fromthe cycloparaffins. structure of high purity and free of any substantialamount of open chain parafilns is separated by fractionation from thecracked product.

For the purpose of simplicity, parts of appa- 1 ratus such as pumps,separators, condensers, etc;

not essential to a complete understanding of the invention have beenomitted from the drawing. Similarly 'fractionating zones depicted in thedrawing'by single fractionators will in actual practice comprise the.use of more than one such A cycloparaftln of hydroaromatic.

2,415,occ

fractionator to effect the indicated separations.

We claim as our invention:

1. Process for the production of cyclohexane from a naphthenic gasolinefraction having a alyst at methylcyclopentane isomerizing condiv tions,thereby converting methylcyclopentane to cyclohexane, separating acyclohexane fraction comprising cyclolzexane and close boiling openchain parafiins from the resulting isomerizate, subjecting saidcyclohexane fraction to thermal cracking conditions at a temperature offrom about 550 C. to about 700 C. and for a period of time of from aboutto about 30 seconds, thereby selectively converting open chain parafllnsto lower boiling hydrocarbons, and fractionally distilling hydrocarbonscomprising cyclohexane from the cracked products.

.2. Process for the production of cyclohexane from a gasoline fractionobtained in the fractionation of naphthenic gasoline and comprisingmethylcyclopentane, cyclohexane and-open chain paraiiins ofsubstantially the same boiling range, which comprisesicontacting saidfraction with an isomerization catalyst comprising a metal halide of theFriedel-Crafts type at methylcyclopentane isomerizing conditions,thereby converting methylcyclopentane to cyclohexane, separating a'cyclohexane fraction comprising cyclohexane and close boiling openchain parafilns from the resulting isomerizate, subjecting saidcyclohexane fraction to thermal selective parafiln cracking conditionsat a temperature of from about 550 C. to about 650 C. and for a periodof time of from about 5 to about 30 seconds, thereby selectivelyconverting open chain paraffins to lower boiling hydrocarbons, andfractionally distilling hydrocarbons comprising cyclohexane from thecracked products. I

3. Process for the production of cyclohexane from a gasoline fractionobtained in the fractionation of naphthenic gasoline and comprisingmethylcyclopentane, cycloheikane and open chain paraiiins ofsubstantially the same boiling range, which comprises contacting saidfraction with an aluminum chlorid isomerization catalyst atmethylcyclopentane isomerizing conditions, there by convertingmethylcyclopentane to cyclohexane, subjecting the resulting isomerizateto thermal cracking conditions at a temperature of from about 550C; toabout 650 C. for a period of time from about to seconds, therebyselectively converting open chain parafiins to lower boilinghydrocarbons, fractionally distilling hydrocarbons comprisingcyclohexane and hydrocarbons comprising methylcyclopentane from thecracked products, and recycling said'hydrocarbons comprisingmethylcyclopentane to said isomerizationstep.

4. Process for the production 01 cyclohexane from a gasoline fractionobtained in the fractionation oi naphthe'nic gasoline and comprisingmethylcyclopentane, cyclohexane and open chain paraflln s ofsubstantially the same boiling range, which comprises contacting saidfraction with an aluminum halide isomerization catalyst atmethylcyclopentane isomerizing conditions, thereby convertingmethylcyclopentane to cyclohexane, subjecting the resulting isomerizateto thermal cracking conditions at a temperature of from about 550 C. toabout 650 C. for a period of time of from about 5 to about 30 seconds,thereby selectively converting upon chain paraflins t0 lower boilinghydrocarbons, fractionally distillii'ig hydrocarbons comprisingcyclohexane and hydrocarbons comprising methylcyclopentane from thecracked products, and recycling said hydrocarbons comprising methylcyclopentane to said isomerization step.

5. Process for the production of cyclohexane from a gasoline fractionobtained in the fractionation of naphthenic gasoline and comprisingmethylcyclopentane, cyclohexane and open chain para-ffins ofsubstantially the same'boiling range, which comprises contacting saidfraction with an isomerization catalyst comprising a metal halide of theFriedel-Crafts type at methylcyclopentane isomerizing conditions,thereby converting methylcyclopentane to cyclohexane, subjecting theresulting isomerizate to thermal cracking conditions at a temperature offrom about 550 C. to about 650 C. and for a period of time of from about5 to about 30 seconds, thereby selectively converting open chainparaffins to lower boiling hydrocarbons, fractionally distillinghydrocarbons comprising cyclohexane and hydrocarbons comprisingmethylcyclopentane from the cracked products, and recycling saidhydrocarbons comprising methylcyclopentane to said isomerization step.o;

6. Process for the production of cyclohexane from a naphthenic gasolinefraction having a maximum boiling point below the'boiling point ofnormal heptane and comprising methylcyclobons comprisingmethylcyclopentane to said isomerization step.

'7. Process for the production of cyclohexane from hydrocarbon mixturescomprisin methylcyclopentane, cyclohexane and open chain paraffins ofsubstantially the same boiling range, which comprises contacting saidfraction with an aluminum halide isomerization catalyst atmethylcyclopentane isomerizing conditions, thereby convertingmethylcyclopentane to cyclohexane, subjecting the resulting isomerizateto thermal cracking conditions at a temperature of from about 550 C. toabout 700" C. and for a period of time of .for about 5 to about 30seconds, thereby selectively converting open chain parafiins to lowerboiling hydrocarbons; fractionally distilling hydrocarbons comprisingcyclohexane and hydrocarbons comprising methylcyclopentane from thecracked products, and recycling said hydrocarbons comprisingmethylcyclopentane to said isomerizatinn step.

, 4 WILLIAM E. ROSS.

PHILIP PEZZAGLIA.

